Yes, the fish live in a big water reserve and people are human after all. It's bad enough to contemplate all the urine in public pools, but the solution for that is to "cleanse" the water with chlorine. CHLORINE! I think it's safer to swim in a pool of uric acid.

I recall that happening in one of the public poos I visited in my youth. They shut it down for a couple weeks because they had to drain the water out, sanitize the system, and fill it up again. I guess accidents happen, and I'm borderline paranoid. But still, it's a disgusting thought.